1. Field of the Invention
The present invention relates to a current balancing module, and more particularly, to a current balancing module utilizing fewer balancing transformers.
2. Description of the Prior Art
In a conventional liquid crystal television utilizing a huge amount of tubes as back light modules, a primary transformer is required for supplying power to all the tubes. The magnitude of each current flowing through each tube is required to be as close as possible for having luminance of each tube be consistent. However, since there are possible differences among the tubes because of fabrication, resistances of the tubes may reveal differences as well. Differences in resistances of the tubes result in differences in magnitudes of currents flowing through the tubes so that consistency and stability in luminance of the tubes fail, and the quality for watching the liquid crystal television is significantly reduced. For neutralizing such defects, more balancing transformers are added to the tubes so as to balance currents flowing through the tubes. However, the added balancing transformers increase the capital, the volume, and power consumption of the liquid crystal television.
Please refer to FIG. 1, which is a diagram of a conventional current balancing module 100 equipping balancing transformers for balancing magnitudes of currents flowing through tubes of a liquid crystal television. As shown in FIG. 1, the current balancing module 100 includes a primary transformer 102, a plurality of capacitors 104, a plurality of tubes 106 respectively corresponding to the plurality of capacitors 104, and a plurality of balancing transformers 108 respectively corresponding to the plurality of tubes 106. The primary transformer 102 is used for raising voltage levels of inputted voltages for lightening the plurality of tubes 106. The plurality of capacitors 104 is utilized for filtering off DC components and harmonic wave components in outputted voltages of the primary transformer 102. The balancing transformer 108 is utilized for modulating the magnitude of the current flowing through each tube 106 with a turns ratio (or a circle ratio) of 1:1 so as to balance the magnitude of the current flowing through each tube 106. However, as shown in FIG. 1, a balancing transformer 108 is required by each tube 106 for cooperating with the modulated current, which creates burdens in volume and fabrication capital. Moreover, the more the number of the plurality of tubes 106 is, the heavier the burden is.
Please refer to FIG. 2, which is a diagram of a conventional current balancing module disclosed in U.S. Pat. No. 6,781,325. As shown in FIG. 2, the DC voltage source 200 is utilized for providing DC voltages for the full bridge circuit 202 so as to transform the DC voltages into square waves, and the transformer 204 is utilized for transforming the voltage level of the DC voltages. A plurality of capacitors C1, C2, C3, . . . , Cn, each of which is successively coupled to the output terminal of the transformer 204, is coupled to a plurality of corresponding tubes CCFL1, CCFL2, CCFL3, . . . , CCFLn respectively in series. A plurality of balancing transformers (or common-mode transformers) CC1, CC2, CC3, . . . , CCn-1 is utilized for balancing magnitudes of currents flowing through the tubes CCFL1, CCFL2, CCFL3, . . . , CCFLn. A passive element module 220 is utilized for receiving a feedback signal, and a controller of the full bridge circuit 202 outputs voltages according to the feedback signal. Therefore, as can be observed in FIG. 2, the magnitudes of currents I1 and I2 are equivalent, and the magnitudes of currents I3 and I4 are equivalent as well. However, though the magnitudes of the currents flowing through the plurality of tubes CCFL1, CCFL2, CCFL3, . . . , CCFLn are balanced to a certain degree, numbers of balancing transformers on certain current paths are not consistent with the most current paths so that the degree of balancing is reduced slightly. Moreover, since the design of the conventional current balancing modules is getting complicated, the volume of utilized elements is also enlarged with the increased number of tubes, and the abovementioned defects cannot be herein neutralized effectively.